The invention relates to a clock apparatus for forming time information of a year, month, day, hour, minute, and second which is used in a small computer system and, more particularly, to a clock apparatus of high precision which can continuously form time information at a high precision.
Hitherto, in a large computer system, time data is displayed by using a binary counter of about 64 bits. According to such a binary counter, initial values are set to, for example, 1990, Jan. 1, 00 hour, 00 minute, 00 second as a Greenwich mean time and time data of year, month, day, hour, minute, and second is calculated from differences between the present time and the time based on the initial values. In such a large computer system, by raising a precision of the binary counter, a precision of the time data can be raised. However, the use of software is indispensable to calculate the time data and such a method is not general in small computer systems such as a workstation and a server.
On the other hand, in an inexpensive computer such as a personal computer or the like, time data is generally displayed by using an IC for a clock (hereinafter, also referred to as a clock IC). The clock IC has therein an oscillator and displays time data of year, month, day, hour, minute, and second by BCD codes. Further, a leap year is also calculated by the clock IC. The clock IC has a high function although its price is low. Those clock ICs have an interface with a general CPU. Therefore, by connecting the commercially available clock IC and the general CPU by a CPU bus, the time data with a high function can be cheaply displayed. The conventional clock IC having therein an oscillator, however, has drawbacks such that the internal oscillator is easily influenced by a temperature change or the like and it is difficult to maintain a stable oscillating frequency and a precision is low.
Under such situations, in small computer systems such as a workstation, server machine, and the like whose number is increasing in recent years, a request of a clock apparatus of a high precision which is almost equivalent to a large computer system is started for file management or the like. The use of such a cheap clock IC, however, cannot satisfy the needs for a high precision. There is also a problem such that it is not practical in a small computer system to use a binary counter of the bit number similar to the large computer and to calculate the time data by software.